This invention relates to a program controlled irrigation system and particularly relates to a multiple program system for controlling the selective operation of irrigation facilities in a plurality of zones of an area to be irrigated periodically.
In the irrigation of large areas such as public parks, estates, golf courses and the like, water is pumped from a supply, through underground conduits and to valves strategically located at stations spaced about the area to be irrigated. A single valve is located at each station and facilitates the control of a sprinkler head to irrigate the area or zone in the vicinity of the particular valve and sprinkler head. Each of the valves are controlled, for example, through an electrical solenoid to facilitate the irrigation process in an orderly fashion.
Control systems have been devised in the past to facilitate the programmed control of irrigation systems under the selective direction of a human operator. Such systems could include, for example, a solid state electronic circuit which permits the operator to select the precise times for the various zones to be irrigated. An example of such a system of this type is disclosed in U.S. Pat. No. 3,869,854 which issued on Mar. 11, 1975. However, the electronic circuit approach is rather elaborate and presents a confusing interface to the operator.
With the advent of low cost microprocessor IC chips, more sophisticated irrigation control systems have evolved as shown in U.S. Pat. No. 4,176,395, which issued on Nov. 29, 1979, U.S. Pat. No. 4,189,776, which issued on Feb. 19, 1979, and U.S. Pat. No. 4,569,020 which issued on Feb. 4, 1986. Each of these systems presents a program-controlled process with selective operator interface through switches and/or pushbuttons on a console and provides the operator with flexibility in selecting and directing a sequential timed irrigation program.
In multiple program systems, two programs are used to control separate portions or modes of the irrigation system respectively to water grass, for example, on the one hand and shrubs, for example, on the other hand. Each program is independent of the other program and can be used only for the particular irrigation mode to which it is dedicated. Therefore, if each program had three available start times, then watering grass or shrubs would each be limited to three starting times. At times, it may be desirable to water certain zones of one mode more frequently than it is desired for the other zones. For example, new grass may be planted in one zone and would require more frequent watering than would normally be required for existing older grass in another zone and, in any event, more frequently than would be required for the shrubs. Therefore, it would be desirable to shift one or more start times from the program for the shrubs and use them temporarily to water more frequently the new grass. Such an option has not been available in the dual mode systems heretofore.
Infrequently, components of the irrigation system may become defective which could result in the draw of excessive current from the power source thereby leading to damage to parts of the system. Typically, at start up, the solenoids draw a high current to operate the solenoid and then drop to a lower level which holds the solenoids in the operated state. If an overcurrent condition occurs, for example because of a short circuit, overheating of and damage to switching elements associated with the solenoids could occur. Shutdown of the system then would be required to protect the system.
On occasion, excessive current is drawn during normal operation of the irrigation system but the current level quickly returns to a normal current level draw. Obviously, it would be desirable not to shut the system down on such temporary occasions of excessive current draw. Also, the irrigation system typically operates on the basis of controlling each valve independently of the other valves whereby, it would be desirable that the entire system not be shut down because of the failure of components associated with one zone and valve.
Notwithstanding the sophistication and capabilities of the above-noted patented systems, and the above-mentioned multiple program systems, there is a need for a multiple program system which is flexible to the extent that start times may be shifted readily from one program and applied to the other program to provide versatility in the irrigation system. Further, there is a need for a program system which will permit continued operation of the system despite an occasional draw of excessive current and will shut down only the defective portion of the system when the excessive current draw is sustained for an undesirable period.